Swell dats

I've been tracking swell data and wave heights for a while now, but I often find myself needing to quickly calculate percentage changes—like figuring out how much bigger today’s swell is compared to last week or estimating the tide drop percentage.

I came across this handy tool: www.percentagescalculator.co.uk, which is great for quick percentage calculations. It’s super straightforward and works for things like swell height comparisons or board volume adjustments.

Does anyone know of an easy way to integrate something like this into a surf forecast spreadsheet or app? Maybe there’s a script or tool some of you use for this sort of thing?